The overall goal of our proposed studies is to establish a powerful selective method for the identification of tumor suppressor genes that are lost during the progression of normal astrocytes to high- grade astrocytomas and glioblastomas. Because tumor suppressors are normal cell products that act to control cell growth and invasiveness, characterization of genes encoding these proteins has tremendous potential for suggesting new modes of cancer therapy. Unfortunately, efforts to identify these genes have been severely hampered by the lack of selective methods. Instead, experimental approaches have had to rely on cytogenetic methods that are slow, laborious and uncertain. We plan to produce cell lines that can be used as assay targets for selective cloning of tumor suppressor cDNAs. These target cell lines will be generated by transfection with plasmid constructs that contain selectable genes under the control of promoters that are responsive to tumor suppressors. Specifically, we will define control sequences that are responsible for activating expression of the human tissue plasminogen activator (tPA) gene and the platelet- derived growth factor-2 (PDGF-2) gene in glial tumors. Target plasmids in which control sequences from the tPA and PDGF-2 genes are linked to selectable genes will be introduced into human glioblastoma cell lines and somatic cell hybrids. We will use selection for or against the selectable gene to dissect the tumorigenic phenotype of these cells. The target glioblastoma cell lines will then be used to selectively identify genes that regulate the tumorigenic phenotype. Identification of genes that control tumorigenicity and invasiveness may lead to new diagnostic and therapeutic approaches and will shed light on normal processes of cell growth and differentiation.